The goal of this project is to characterize the host immunological responses to infection with G. lamblia. These responses may modulate the clinical course demonstrated by various subsets of patients with giardiasis. We are therefore examining giardiasis patients for the presence of anti-G. lamblia antibodies in serum, salivary duct secretious and intestinal fluid by an enzyme-linked immunsorbent assay. IgG anti-G. lamblia antibodies have been demonstrated in serum. The immunoreactive antigens to which these antibodies are directed are being characterized by a combination of SDS gel electrophoresis and Staph A radioimmunoassay. To examine the cellular immune responses in giardiasis patients, we are studying in vitro lymphocyte transformation in response to G. lamblia trophozoite antigen. The effector mechanism of cellular interaction with G. lamblia is being investigated with spontaneous cell-mediated and antibody-dependent cytotoxicity assays. Thus, characterizing the humoral and cellular immunological responses in patients with giardiasis may elucidate how host defense mechanisms modulate clinical giardiasis.